The present invention relates to a process for the preparation of a rubber laminate. More specifically, the present invention relates to a process for the preparation of a laminate comprising a layer of a cured fluororubber and a layer of a cured epoxy group-containing acrylate rubber, which are tightly bonded to each other.
The properties required of rubber materials have recently become severe especially in industrial uses and the automobile-related industries.
A fluororubber is excellent in such properties as heat resistance, oil resistance, chemical resistance, solvent resistance and gas barrier property, so that it is widely used in various field where these excellent properties can be utilized.
Although the fluororubber has these excellent properties, it is more expensive than an acrylonitrilebutadiene rubber and an epoxy group-containing acrylate rubber (hereinafter referred to as "AR") and is defective in that the cold resistance is poor.
Therefore, a laminate comprising a layer of an ordinary rubber composition formed on a layer of a fluororubber composition having the above-mentioned excellent properties has attracted attention in the art.
In case of hoses and diaphragms, the fluororubber is most suitable for the inner layer in contact with an oil, gasoline or a chemical, but its properties are too good for the outer layer and AR is sufficient for the outer layer from the viewpoint of the heat resistance, oil resistance or cost.
Cure-bonding of the fluororubber to AR is very difficult according to customary procedures or the bonding force is so weak that no laminate having an excellent bonding force has been provided.
As the means for eliminating this disadvantage, there have been proposed a process in which a guanidine compound is added as a curing agent to AR (see Japanese Patent Application Kokai Publication No. 61-171981 and a process in which a peroxide and a crosslinking assistant are added (see Japanese Patent Application Kokai Publication No. 61-179735). However, in these processes, the design of the rubber composition is restricted by the curing system used or the like, and the physical properties of laminates formed according to the teachings of these patent publications are not fully satisfactory.